Ultrafast Electric Switching of Brookite TiO2 Nanorods with a Permanent Dipole Moment at High Concentrations

Abstract

Transient electric birefringence measurements are used to show that brookite titania nanorods dispersed in the apolar liquid butylbenzene possess a large permanent dipole moment of 516 debye (rod length: 39 nm, diameter: 4.1 nm). This dipole moment makes the particles highly susceptible to applied electric fields. Isotropic dispersions at high volume fractions of up to 20% nanorods are aligned on a time scale of tens of microseconds at low field strengths. Alignment becomes nearly complete at a field strength of around 10 V/µm. It is shown that the birefringence of these dispersions is large enough that light transmission can be switched on and off in thin film cells of 150 µm thickness. These properties make brookite nanorod dispersions promising as the active material in optoelectronic applications.